Comparative light and electron microscopic study of retinal histogenesis in normal and rd mutant mice

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Mice, homozygous for the mutant gene rd show selective degeneration of the photoreceptor cells after their initial differentiation. Phenotypic expression in the mutant and in normal mice was studied by light and electron microscopy. The sequential emergence of developmental deviations in the mutant retina falls into three categories. First, predegenerative differences are manifest within the photoreceptor cells during 4–8 days after birth in retarded growth of the inner segments, reduced outer segment production, delayed development of the outer plexiform layer and slower segregation of the perikarya. Next, degenerative changes are recognized from 6 day onwards with swelling and vacuolization of the Golgi cisternae in the inner segments followed by cytolytic alterations affecting the ultrastructure of the entire cell. Lastly, with increasing loss of photoreceptor cells post-degenerative effects are seen in deepening of the basal infoldings and microvilli of the pigment epithelium and increase of Müller's fibres. The progress of degeneration in the mutant retina corresponds to the phase of rapid growth of the Golgi apparatus and rod outer segments in the normal retina. The role of the Golgi apparatus in the differentiation of the photoreceptor cells and its relation to the expression of the rd gene are discussed.

Supported in part by grant No. A-6207 from the National Research Council of Canada.
Authors' thanks are due to Professor Dr. J. Moll for critical reading of the manuscript, to Mr. Ian Atkinson, Mr. R. K. Hawkins and Miss A. de Ruiter for expert technical assistance; to Mr. W. van den Oudenalder and Miss P.C. Delfos for help in photography and to Mrs. L.C. Boonstra for typing the manuscript.